Electrodeless light bulb type fluorescent lamp and discharge lamp lighting device

ABSTRACT

An electrodeless self-ballasted fluorescent lamp includes an electrodeless fluorescent lamp  3 , a ballast circuit  4  and a lamp base which are formed as one unit. The ballast circuit  4  includes: an AC-DC converter  5 ; a DC-AC converter  6  formed so as to intermittently drive the electrodeless fluorescent lamp  3 ; and a dimming controller  7  formed so as to detect the turn-on of a phase-controlled AC voltage and output an intermittent command signal for changing the ratio between an operating period and an extinguishing period to the DC-AC converter  6 . Furthermore, the dimming controller  7  is formed so as to output a signal for extinguishing the electrodeless fluorescent lamp  3  before the operation thereof becomes unstable.

TECHNICAL FIELD

[0001] The present invention relates to discharge lamp operatingdevices. In particular, the present invention relates to electrodelessself-ballasted fluorescent lamps in which electrodeless fluorescentlamps can be dimmed.

BACKGROUND ART

[0002] A fluorescent lamp has been widely used from global environmentalprotection and economic standpoints because it has a higher degree ofefficiency and a longer life as compared with an incandescent lamp. Inrecent years, as an economical light source, an electrodelessself-ballasted fluorescent lamp having no electrode has been attractingmuch attention since its life is several times longer than that of aconventional self-ballasted fluorescent lamp having electrodes, and thedemand for an electrodeless self-ballasted fluorescent lamp is on theincrease.

[0003] Furthermore, a self-ballasted fluorescent lamp in which afluorescent lamp and a ballast circuit therefor are integrally formed isbecoming a focus of attention as an energy-saving light source inhouses, hotels, restaurants or the like, and is now becoming widespreadbecause the self-ballasted fluorescent lamp can be readily used as it isin place of an incandescent lamp. In addition to the self-ballastedfluorescent lamp of this type having electrodes, the self-ballastedfluorescent lamp of this type having no electrode is also underdevelopment.

[0004] With the widespread use of the self-ballasted fluorescent lamp,as with a dimmable incandescent lamp, the need for dimming of theself-ballasted fluorescent lamp is being created. To be more specific,in houses or hotels, people carry out various daily living activitiessuch as reading or spending a happy time with family, and in order toachieve a comfortable light environment adapted to these daily livingactivities, a user desires brightness suitable to each situation andseeks a function that realizes such brightness. Since an incandescentlamp does not emit light by discharge, it can be easily dimmed by merelyadjusting electric power supplied thereto. On the other hand, since afluorescent lamp emits light by discharge, it is difficult to implementa dimmable fluorescent lamp that can be practically used by merelyadjusting electric power supplied thereto like an incandescent lamp.

[0005] Lately, in response to a need for a user to change brightnessutilizing an already-known incandescent lamp dimmer as with anincandescent lamp, a self-ballasted fluorescent lamp with electrodes,which is connected to an incandescent lamp dimmer and allows dimmableoperation, has been developed (see Japanese Unexamined PatentPublication No. 1999-111486, for example). However, the fact is that anelectrodeless self-ballasted fluorescent lamp which is dimmable has notyet developed.

[0006] Besides, a self-ballasted fluorescent lamp having electrodesrequires preheating of the electrodes for the discharge of electronstherefrom, and thus needs a voltage of a certain level. Therefore, ifdeeper dimming is carried out using a fluorescent lamp havingelectrodes, extinguishing occurs at the instant when a dimming voltagebecomes lower than a voltage required for preheating of the electrodes,thus making it impossible to carry out smooth dimming.

[0007] The present applicant has already developed an electrodelessself-ballasted fluorescent lamp that is dimmable, and succeeded incompleting such a lamp; however, this lamp still has inadequacies. Forexample, undesired extinguishing or flickering of the lamp occurs whenlow level dimming is carried out, and therefore, smooth dimmingoperation might not be achieved.

[0008] The present invention has been made in view of theabove-described problems, and its main object is to provide anelectrodeless self-ballasted fluorescent lamp and a discharge lampoperating device which achieve smooth dimming operation.

DISCLOSURE OF THE INVENTION

[0009] An inventive electrodeless self-ballasted fluorescent lampincludes: an electrodeless fluorescent lamp; a ballast circuit forapplying a high-frequency voltage to the electrodeless fluorescent lamp;and a lamp base electrically connected to the ballast circuit, whereinthe electrodeless fluorescent lamp, the ballast circuit and the lampbase are formed as one unit, wherein the ballast circuit includes: anAC-DC converter for converting a phase-controlled AC voltage into a DCvoltage; a DC-AC converter for converting the DC voltage into ahigh-frequency voltage, the DC-AC converter being formed so as tointermittently drive the electrodeless fluorescent lamp due to theexistence of an operating period during which the high-frequency voltageis applied to the electrodeless fluorescent lamp so that theelectrodeless fluorescent lamp is operated, and an extinguishing periodduring which the generation of the high-frequency voltage is stopped sothat the electrodeless fluorescent lamp is extinguished; and a dimmingcontroller for detecting the turn-on of the phase-controlled AC voltageand for outputting an intermittent command signal that changes the ratiobetween the operating period and the extinguishing period to the DC-ACconverter, and wherein the dimming controller is formed so as to outputa signal for extinguishing the electrodeless fluorescent lamp before theoperation thereof becomes unstable.

[0010] In one preferred embodiment, the dimming controller includes: afirst dimming control signal input section and a second dimming controlsignal input section; a sawtooth wave generator for generating asawtooth wave; and a dimming command signal generator for generating adimming command signal, the first dimming control signal input sectionis connected to the sawtooth wave generator via a photo coupler, and thesecond dimming control signal input section is connected to the dimmingcommand signal generator.

[0011] In one preferred embodiment, the sawtooth wave generator and thedimming command signal generator are connected to a comparator.

[0012] In one preferred embodiment, the dimming controller is furtherformed so as to output a signal for synchronizing the timing of theturn-on with that of the operation of the lamp intermittently driven bythe DC-AC converter.

[0013] In one preferred embodiment, the dimming controller has asawtooth wave generator including a differentiating circuit thatincludes a capacitor and a resistor, the differentiating circuit isconnected to a collector terminal of a transistor for generating a pulsewave synchronized with the turn-on and turn-off of the phase-controlledAC voltage, an output terminal of the differentiating circuit isconnected with an anode of a diode while a cathode of the diode isconnected with a base terminal of a transistor for discharge, an emitterterminal of the transistor for discharge is connected with a diode forpotential adjustment, and a capacitor for charge and discharge isconnected between the emitter terminal and collector terminal of thetransistor for discharge, thus allowing the generation of a sawtoothwave synchronized with the turn-on of the phase-controlled voltage.

[0014] In one preferred embodiment, the phase-controlled AC voltage isan output voltage of a dimmer which has been phase-controlled by thedimmer.

[0015] An inventive discharge lamp operating device includes: adischarge lamp; an AC-DC converter for converting a phase-controlled ACvoltage into a DC voltage; a DC-AC converter for converting the DCvoltage into a high-frequency voltage, the DC-AC converterintermittently driving the discharge lamp due to the existence of anoperating period during which the high-frequency voltage is applied tothe discharge lamp so that the discharge lamp is operated, and anextinguishing period during which the generation of the high-frequencyvoltage is stopped so that the discharge lamp is extinguished; and adimming controller for detecting the turn-on of the phase-controlled ACvoltage and for outputting an intermittent command signal that changesthe ratio between the operating period and the extinguishing period tothe DC-AC converter, wherein the discharge lamp is an electrodelessdischarge lamp, and wherein the dimming controller is formed so as tooutput a signal for extinguishing the discharge lamp before theoperation thereof becomes unstable.

[0016] In one preferred embodiment, the dimming controller is furtherformed so as to output a signal for synchronizing the timing of theturn-on with that of the operation of the lamp intermittently driven bythe DC-AC converter.

[0017] In one preferred embodiment, the discharge lamp has a dischargebulb with a recessed portion, and an induction coil is inserted into therecessed portion of the discharge bulb.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a diagram showing the circuit configuration of anelectrodeless self-ballasted fluorescent lamp (or a discharge lampoperating device) according to a first embodiment of the presentinvention.

[0019]FIG. 2 is a cross-sectional view schematically showing thestructure of the electrodeless self-ballasted fluorescent lamp of thefirst embodiment.

[0020]FIG. 3 illustrates waveform charts showing various waveforms inthe configuration of the first embodiment.

[0021]FIG. 4(a) illustrates waveform charts showing the relationshipbetween phase-control angle and on duty ratio, and FIG. 4(b) is a graphshowing the relationship between the phase-control angle and the on dutyratio.

[0022]FIG. 5 is a diagram showing the circuit configuration of adischarge lamp operating device according to a second embodiment of thepresent invention.

[0023]FIG. 6 is a diagram showing the circuit configuration of adischarge lamp operating device according to an embodiment forreference.

[0024]FIG. 7 is a diagram showing the circuit configuration of anasynchronous type discharge lamp operating device.

[0025]FIG. 8 illustrates various waveform charts concerning thedischarge lamp operating device shown in FIG. 7.

[0026]FIG. 9 illustrates various waveforms charts concerning thedischarge lamp operating device shown in FIG. 7.

BEST MODE FOR CARRYING-OUT OF THE INVENTION

[0027] Hereinafter, embodiments of the present invention will bedescribed with reference to the drawings. In the following drawings, forsimplification of the description, the same constituting elements havingsubstantially identical functions are identified by the same referencecharacters. It should be noted that the present invention is not limitedto the following embodiments.

EMBODIMENT 1

[0028]FIG. 1 schematically shows the configuration of a discharge lampoperating device according to a first embodiment of the presentinvention. And FIG. 2 is a cross-sectional view of the discharge lampoperating device of the present embodiment implemented as anelectrodeless self-ballasted fluorescent lamp.

[0029] The electrodeless self-ballasted fluorescent lamp of the presentembodiment includes: an electrodeless fluorescent lamp 3; a ballastcircuit 4 (circuit board 54) for applying a high-frequency voltage tothe electrodeless fluorescent lamp 3; and a lamp base 56 electricallyconnected to the ballast circuit 4 (circuit board 54). The circuit board54 shown in FIG. 2 is formed with the ballast circuit 4 shown in FIG. 1.Specifically, the circuit board 54 is formed with wirings provided asshown in the ballast circuit 4, and is attached with respective circuitcomponents.

[0030] As shown in FIG. 2, in the electrodeless self-ballastedfluorescent lamp, the electrodeless fluorescent lamp 3, the ballastcircuit 4 (circuit board 54) and the lamp base 56 are formed as oneunit. In this embodiment, the electrodeless fluorescent lamp 3 includesa discharge bulb 17 having a recessed portion 17 a, and an inductioncoil 16 made up of a core 16 a and a coil 16 b is inserted into therecessed portion 17 a. The coil 16 b is electrically connected to thecircuit board 54, and a cover 55 for accommodating the circuit board 54is provided around the circuit board 54. The lamp base 56 (e.g., E26type for incandescent lamp) is attached to a lower part of the cover 55,and is electrically connected to the circuit board 54. By screwing thelamp base 56 into a socket for an incandescent lamp, the supply ofelectric power is allowed, and thus the operation of the electrodelessfluorescent lamp 3 is enabled. An AC voltage inputted through the lampbase 56 is an AC voltage that is phase-controlled by, for example, anexternal phase controller (such as a dimmer 2 shown in FIG. 1, typicallya dimmer for an incandescent lamp).

[0031] The ballast circuit 4 shown in FIG. 1 includes: an AC-DCconverter 5 for converting a phase-controlled AC voltage into a DCvoltage; a DC-AC converter 6 for converting the DC voltage, which hasbeen converted in the AC-DC converter 5, into a high-frequency voltage;and a dimming controller 7. It should be noted that the AC-DC converter5, the DC-AC converter 6 and the dimming controller 7 may be called aconverter for smoothing an AC voltage into a DC voltage, an inverter anda detector (detection means), respectively.

[0032] The ballast circuit 4 is connected to a commercial power supply 1via the dimmer 2 for carrying out the phase control of a voltagesupplied from the commercial power supply 1. Furthermore, the ballastcircuit 4 operates the electrodeless fluorescent lamp 3 in response tothe turn-on of the voltage phase-controlled in the dimmer 2. Thecommercial power supply 1 is an AC power supply for 60Hz and 100V, forexample, and the dimmer 2 is connected thereto. The dimmer 2 is one thatcarries out phase control using a triac, and a commercially availabledimmer for an incandescent lamp can be typically used as the dimmer 2.

[0033] The AC-DC converter 5 converts the phase-controlled voltage,supplied from the dimmer 2, into a DC voltage. As the AC-DC converter 5,one that utilizes a diode bridge and a smoothing capacitor, for example,may be used. The DC-AC converter 6 is formed so as to intermittentlydrive the electrodeless fluorescent lamp 3 due to the existence of anoperating period during which the converted high-frequency voltage isapplied to the electrodeless fluorescent lamp 3 so that theelectrodeless fluorescent lamp 3 is operated, and an extinguishingperiod during which the generation of the high-frequency voltage isstopped so that the electrodeless fluorescent lamp 3 is extinguished.

[0034] As shown in FIG. 1, the DC-AC converter 6 of the presentembodiment includes: an oscillator 8; a switching circuit 9; a drivingcircuit 10; switching elements (MOSFETs 11 and 12); a resonant inductor13; and resonant capacitors 14 and 15. Specifically, the induction coil16 is connected to the resonant capacitor 15 in series, and furthermore,a series circuit of the induction coil 16 and the resonant capacitor 15is connected to the resonant capacitor 14 in parallel. In thisembodiment, the electrodeless fluorescent lamp 3 is formed by theinduction coil 16 and the electrodeless discharge bulb 17. The inductioncoil 16 is made up of the ferrite core 16 a and the coil 16 b, and isplaced into the recessed portion 17 a of the discharge bulb 17.

[0035] The dimming controller 7 is formed so as to detect the turn-on ofthe phase-controlled AC voltage, and so as to output an intermittentcommand signal for changing the ratio between the operating period andextinguishing period to the DC-AC converter 6 (in particular, theswitching circuit 9). Further, the dimming controller 7 is formed so asto output a signal for extinguishing the electrodeless fluorescent lamp3 before the operation thereof becomes unstable. Furthermore, thedimming controller 7 of the present embodiment is formed so as to outputa signal for synchronizing the timing of the turn-on with that of theoperation of the electrodeless fluorescent lamp 3 intermittently drivenby the DC-AC converter 6. In other words, the dimming controller 7 canbe called a synchronous type duty modulator.

[0036] As shown in FIG. 1, the dimming controller 7 of the presentembodiment includes: a dimming control signal input section A 18; aphoto coupler 19; a sawtooth wave generator 20; a dimming command signalinput section B 21; a dimming command signal generator 22; and acomparator 23 (e.g., a comparator formed using an operationalamplifier). By using the photo coupler 19, the dimming control signalinput section A 18 and the sawtooth wave generator 20 can be insulatedfrom each other; therefore, noise reduction can be achieved, andperformance increase can be attained. A sawtooth wave is generated usingthe dimming control signal input section A 18, to which the voltagephase-controlled by the dimmer 2 is inputted, the photo coupler 19 andthe sawtooth wave generator 20. Furthermore, a dimming command signal isgenerated using the dimming command signal input section B 21 and thedimming command signal generator 22, and then, the sawtooth wave is sentto the non-inverting input terminal of the comparator 23 while thedimming command signal is sent to the inverting input terminal of thecomparator 23; thus, from the resulting voltage difference, thecomparator 23 generates an intermittent dimming signal.

[0037] Hereinafter, operations to be performed in the configuration ofthe first embodiment will be briefly described.

[0038] First, an output voltage from the commercial power supply 1 isphase-controlled in the dimmer 2, and then the phase-controlled ACvoltage is converted into a DC voltage in the AC-DC converter 5.

[0039] Next, the driving circuit 10 for the MOSFETs 11 and 12 of theDC-AC converter 6 is driven in response to an output at a drivingfrequency f1 (Hz) from the oscillator 8. By allowing the two MOSFETs 11and 12 to alternately turn on and off, the DC voltage smoothed by theAC-DC converter 5 is converted into a high-frequency voltage.

[0040] Subsequently, the high-frequency voltage is applied to a resonantcircuit made up of the resonant inductor 13, the resonant capacitors 14and 15, and the induction coil 16. Due to a current flowing through theinduction coil 16, an AC electromagnetic field is generated within theelectrodeless discharge bulb 17, and an energy supplied by the ACelectromagnetic filed causes excitation of a light-emitting gas (notshown) enclosed within the electrodeless discharge bulb, resulting inlight emission. As the light-emitting gas, for example, mercury,krypton, xenon or a gas mixture thereof may be used. Optionally, a gascontaining only a rare gas but no mercury may also be used.

[0041] Note that, in that case, the timing of the turn-on of thephase-controlled voltage is detected by the dimming controller 7, andthe turn-on of the intermittent command signal synchronized with theturn-on of the phase-controlled voltage occurs in the dimming controller7 and is transmitted to the switching circuit 9. Over the period duringwhich the intermittent command signal is transmitted to the switchingcircuit 9 (i.e., the on period, or the operating period of theelectrodeless fluorescent lamp 3), the switching circuit is turned on,and the driving circuit 10 for the MOSFETs 11 and 12 is turned on. Tothe contrary, over the period during which the intermittent commandsignal is not transmitted to the switching circuit 9 (i.e., the offperiod, or the extinguishing period of the electrodeless fluorescentlamp 3), the switching circuit 9 is turned off, and the driving circuit10 for the MOSFETs 11 and 12 is turned off. During the on period of theswitching circuit 9, the turning on and turning off of the MOSFETs 11and 12 are alternately repeated with the driving frequency f1 (Hz). Inaccordance with a variation in the conduction period of the voltagephase-controlled by the dimmer 2, the ratio between the on period andoff period of the switching circuit 9, determined by the intermittentcommand signal from the dimming controller 7, is changed, and inaccordance with this change, the ratio between the on period and offperiod of the MOSFETs 11 and 12 (which will be herein called a dutyratio) is varied. That is, the variation in the duty ratio causes achange in an electric energy input to the electrodeless fluorescent lamp3, thus carrying out dimming of the electrodeless fluorescent lamp 3.

[0042] Hereinafter, the operation of the dimming controller 7 will bedescribed in detail with reference to also FIG. 3. FIG. 3 shows therelationships among a phase-controlled voltage a, a turn-on detectionsignal b, a sawtooth wave c, a dimming command signal d, an intermittentcommand signal e, and a light output f, wherein in the five charts, eachhorizontal axis is a time axis, and the time axis serves as a commonmeasure in the respective charts.

[0043] The phase-controlled voltage a in FIG. 3 is first inputted to thedimming control signal input section A 18 in the dimming controller 7shown in FIG. 1. Then, the phase-controlled voltage a is full-waverectified in the dimming control signal input section A 18, and issubsequently reduced to a voltage (e.g., 2V) appropriate for the drivingof the photo coupler 19 and applied to the photo coupler 19.

[0044] Concurrently with the turn-on of the voltage phase-controlled inthe dimmer 2, there occurs the turn-on of the full-wave rectifiedvoltage inputted to the photo coupler 19. Next, after the rise time ofthe photo coupler 19 (e.g., 20 μs), a light emitting diode incorporatedinto the photo coupler 19 emits light.

[0045] Due to the light emission of the diode, a pulse wave synchronizedwith the turn-on and turn-off of the phase-controlled voltage a isoutputted from a transistor that forms a part of the photo coupler 19.Then, due to the existence of an IC such as a monostable multivibrator,the sawtooth wave generator 20 outputs the turn-on detection signal bsynchronized only with the turn-on of the phase-controlled voltage a byusing, as a trigger input, the turn-on signal from the photo coupler 19.

[0046] The turn-on detection signal b is sent to a base terminal of thetransistor, a capacitor connected between an emitter and a collector ofthe transistor is charged and discharged, and the sawtooth wave c isoutputted.

[0047] On the other hand, the phase-controlled voltage a is inputted tothe dimming control signal input section B 21 of the dimming controller7 shown in FIG. 1, and is half-wave rectified by the dimming controlsignal input section B 21. Then, in the dimming command signal generator22, the half-wave rectified portion of the phase-controlled voltage isintegrated, and thereafter the dimming command signal d is outputted.

[0048] The comparator 23 receives, at its non-inverting input terminaland inverting input terminal, the sawtooth wave c and the dimmingcommand signal d, respectively, and outputs the intermittent commandsignal e in accordance with the potential difference between both thesignals.

[0049] Thereafter, the intermittent command signal e is transmitted tothe switching circuit 9, and during the on period of the intermittentcommand signal e, the MOSFETs 11 and 12 of the DC-AC converter 6 aredriven with the driving frequency f1 (Hz), thereby obtaining the lightoutput f.

[0050] The on state of the intermittent command signal e is maintaineduntil the potential of the sawtooth wave c becomes higher than that ofthe dimming command signal d. Upon inversion of the potentialrelationship, the intermittent command signal e becomes off, which istransmitted to the switching circuit 9, and the driving of the MOSFETs11 and 12 is stopped, thus extinguishing light.

[0051] In this manner, the duty of the intermittent command signal e isdetermined by the potential relationship between the potential of thesawtooth wave c and that of the dimming command signal d, andfurthermore, the operation during the on period of the intermittentcommand signal and the extinguishing during the off period of theintermittent command signal are repeated, thus enabling intermittentdimming.

[0052] In addition, the sawtooth wave generator 20 is set such that acertain potential is secured even if electrical charges of the capacitorfor charge and discharge are completely discharged. For example, ifthree diodes, each having a forward voltage of about 0.6V, are connectedto the emitter terminal, the minimum potential of the sawtooth wave cbecomes about 1.8V. Besides, since the charge and discharge are carriedout using, as a trigger, the signal of the turn-on of thephase-controlled voltage, the sawtooth wave maintains a constantwaveform even if the conduction angle of the phase-controlled voltage ischanged. On the other hand, since the half-wave rectified portion of thephase-controlled voltage is integrated, the potential of the dimmingcommand signal d is changed, and if the potential of the dimming commandsignal d becomes equal to or lower than a certain potential (minimumpotential) of the sawtooth wave c, all the intermittent command signalse enter the off period. And at or below a certain conduction angle ofthe phase-controlled voltage (i.e., at or below a conduction angle atwhich the minimum potential of the sawtooth wave c and the potential ofthe dimming command signal d become equal to each other), the driving ofthe MOSFETs 11 and 12 of the DC-AC converter 6 is stopped and thus thelight is extinguished.

[0053] Thus, by adjusting the minimum potential of the sawtooth wave,the driving of the MOSFETs 11 and 12 of the DC-AC converter 6 can bestopped and the light can be extinguished at an arbitrary phase level ofthe phase-controlled voltage from the dimmer 2.

[0054] Hereinafter, with reference to also FIG. 4, description will bemade about the relationship between the conduction angle of thephase-controlled voltage, and the on duty of the intermittent commandsignal in the present embodiment.

[0055]FIG. 4(a) shows the relationship between the phase-controlledvoltage a and the intermittent command signal e. In FIG. 4(a), (i)illustrates the case where the phase-control angle is about 0°, (ii)illustrates the case where the phase-control angle is about 90°, and(iii) illustrates the case where the phase-control angle is about 120°.Furthermore, in the six charts showing the waveforms of thephase-controlled voltage a and the intermittent command signal b, eachhorizontal axis is a time axis, and the time axis serves as a commonmeasure in the respective charts.

[0056] The phase-controlled voltage a shown in FIG. 4(a) is firstinputted to the dimming control signal input section 8 of the dimmingcontroller 7 shown in FIG. 1, and is rectified in the dimming controlsignal input section A 18. Next, the intermittent command signal b istransmitted to the switching circuit 9 via the intermittent commandsignal generator 19, and thus the MOSFETs 11 and 12 of the DC-ACconverter 6 are driven with the driving frequency f1 (Hz).

[0057] In the present embodiment, as can be seen from (iii) in FIG.4(a), even if the phase-controlled voltage a is remaining, theintermittent command signal e is off. That is, before the operation ofthe electrodeless fluorescent lamp 3 becomes unstable, the dimmingcontroller 7 outputs a signal for extinguishing the electrodelessfluorescent lamp 3.

[0058]FIG. 4(b) shows the relationship between the phase-control angleand on duty ratio, and the horizontal axis represents the phase-controlangle [degree] while the vertical axis represents the on duty ratio. InFIG. 4(b), (I) signifies an electric energy supply insufficient regionwhere dimming is carried out at a deeper level by the dimmer 2, and thepresent inventors confirmed that in this region, a voltage applied tothe fluorescent lamp 3 is low, and a phenomenon such as undesiredextinguishing or flickering might occur.

[0059] The electric energy supply insufficient region (I) covers therange of the phase-control angle equal to or higher than 120°. If thephase-control angle becomes equal to or higher than 120°, flickering islikely to occur. If the phase-control angle becomes equal to or higherthan 150°, many people feel uncomfortable. And if deeper dimming iscarried out, the light is undesirably extinguished. In some cases, dueto variations in the characteristics of electrodeless self-ballastedfluorescent lamps, flickering does not occur even if the phase-controlangle exceeds 120°; however, in order to surely prevent flickering forall the lamps, it is preferable that the electric energy supplyinsufficient region (I) covers the range of the phase-control angleequal to or higher than 120°.

[0060] In addition, during the period over which the phase-control anglechanges from 0° to 120°, i.e., until the on duty ratio changes from 100to 0, the on duty ratio is linearly decreased in accordance with anincrease in the phase-control angle. That is, in this range, anapproximate linear function relationship with a negative slope isestablished between the phase-control angle and the on duty ratio.Therefore, when the dimmer is operated, in this range, the lightemission output of the lamp is also substantially linearly decreased inaccordance with an increase in the approximate phase-control angle, andthus the dimming of the lamp can be carried out with ease.

[0061] In this embodiment, before the electric energy supplyinsufficient region (I) is reached, the on duty ratio of theintermittent command signal e is reduced to 0, and the electrodelessfluorescent lamp 3 is extinguished; therefore, a problem such asflickering or operation failure does not occur.

[0062] Note that the on time width t of the monostable multivibrator canbe freely set by the equation, t=0.693 RC (where R and C represent aresistor and a capacitor which are added to the IC, respectively). Inthe case where the on time width is long, even after the electricalcharges of the capacitor for charge and discharge are completelydischarged, the charge will not start, and the off period (minimumpotential period) of the sawtooth wave c becomes long. This narrows theadjustment range of the on period of the intermittent command signalresulting from the voltage difference between the sawtooth wave c andthe dimming command signal d; as a result, the adjustment range of thedriving period of the MOSFETs is also narrowed, and thus a low dimminglevel cannot be achieved. Accordingly, the shorter the on time width ofthe monostable multivibrator, the wider the adjustment range of the onperiod of the intermittent dimming command signal. On the other hand,since the sawtooth wave is a signal resulting from the charge anddischarge of electrical charges, a sufficient discharge time has to beset in order to obtain a stable sawtooth wave. Therefore, if the maximumoutput level of the sawtooth wave is about 4V, for example, thedischarge time is preferably about 0.4 ms upon due consideration.

[0063] In the case where a hysteretic comparator is used instead of thecomparator 23, unneeded output inversion is not carried out even if aninput signal includes noise, and as a result, the dimming that causes noflickering can be carried out.

[0064] As described above, in the electrodeless self-ballastedfluorescent lamp of the first embodiment, the dimming controller 7 isformed so as to output a signal for extinguishing the electrodelessfluorescent lamp 3 before the operation thereof becomes unstable; thus,deep dimming (i.e., low level dimming) can be stably carried out. Thatis, the turn-on of the AC voltage phase-controlled in an incandescentlamp dimmer, for example, can be accurately detected so as to start thedriving, and in addition, the driving can be stopped within the range inwhich an application voltage required for the start of operation of thefluorescent lamp is obtainable, thus achieving smooth dimming operationthat causes no flickering.

[0065] It should be noted that in the present embodiment, theconfiguration of the electrodeless self-ballasted fluorescent lamp hasbeen described; however, the present embodiment may also be applied toan electrodeless self-ballasted discharge lamp having no fluorescentmaterial. In other words, the present embodiment may be applied to adischarge lamp such as a lamp for sterilization in which no fluorescentmaterial is applied to its discharge bulb. Furthermore, the applicationis not limited to general illumination but may include, for example, theoperation of a lamp for emitting rays of light for a person's health,which has an action spectrum effective against erythema or effective ingenerating vitamin D, or a lamp for growing plants, which has an actionspectrum effective in enabling photosynthesis or morphogenesis ofplants. In addition, as can be understood from the circuit diagram shownin FIG. 1, the configuration of the present embodiment is not limited toa self-ballasted lamp operating device, but may be applied to adischarge lamp operating device (i.e., an electrodeless discharge lampoperating device) in which the electrodeless fluorescent lamp 3 and theballast circuit 4 are independently provided.

[0066] Hereinafter, a brief description will be made about the frequencyof the high-frequency voltage applied from the ballast circuit 4 to theelectrodeless fluorescent lamp 3 in the electrodeless self-ballastedfluorescent lamp of the present embodiment. The frequency in the presentembodiment is in a relatively low frequency range of 1 MHz or less(e.g., 50 kHz to 500 kHz) as compared with an ISM frequency band of13.56 MHz or several MHz which is practically and generally utilized.The frequency in such a low frequency range is used because of thefollowing reasons. First, if the lamp is operated in a relatively highfrequency range such as 13.56 MHz or several MHz, a noise filter forsuppressing line noise generated from a high-frequency power supplycircuit within the ballast circuit (circuit board) is increased in size,which undesirably increases the volume of the high-frequency powersupply circuit. Further, supposing that noise radiated or propagatedfrom the lamp is high-frequency noise, since laws and regulations arevery strictly restricting the high-frequency noise, an expensive shieldhas to be provided and utilized in order to meet the restrictions, whichpresents a serious obstacle in achieving cost reduction. To thecontrary, if the lamp is operated in a frequency range of about 1 MHz to50 kHz, inexpensive general-purpose products, which are used aselectronic components for general electronic equipment, can be utilizedas components for forming the high-frequency power supply circuit; inaddition, since the use of small-sized components is enabled, not onlycost reduction but also size reduction can be achieved, thus obtainingconsiderable advantages. It is to be noted that the electrodelessfluorescent lamp of the present embodiment does not have to be operatedat a frequency of 1 MHz or less, but may alternatively be operated in afrequency range of 13.56 MHz or several MHz, for example.

EMBODIMENT 2

[0067] Hereinafter, a second embodiment of the present invention will bedescribed with reference to FIG. 5. Although the configuration of adischarge lamp operating device of the present embodiment is similar tothat described in the first embodiment, a sawtooth wave generator 20 fordetecting the turn-on of a phase-controlled voltage is formeddifferently from the counterpart in the first embodiment, and can beformed inexpensively without using any IC in the configuration of thepresent embodiment.

[0068]FIG. 5 shows a circuit for detecting the turn-on of aphase-controlled voltage in the present embodiment, and in particularshows the configuration of the sawtooth wave generator 20. It should benoted that the same constituting elements as the counterparts describedin the first embodiment are identified by the same reference characters,and the further description thereof will be omitted.

[0069] The sawtooth wave generator 20 shown in FIG. 5 has: adifferentiating circuit 201; a diode 202; a transistor 203; and acapacitor 204, and the differentiating circuit 201 includes a capacitorand a resistor. The sawtooth wave generator 20 is connected to a dimmingcontrol signal input section A 18 via a photo coupler 19, the dimmingcontrol signal input section A 18 is connected to a dimmer 2, and thedimmer 2 is electrically connected to a commercial power supply 1. Itshould be noted that a transistor may be provided between the photocoupler 19 and the differentiating circuit 201 for currentamplification.

[0070] In the present embodiment, the differentiating circuit 201 isconnected to a collector terminal of the transistor of the photo coupler19, which generates a pulse wave synchronized with the turn-on andturn-off of a phase-controlled AC voltage. An output terminal of thedifferentiating circuit 201 is connected with an anode of the diode 202,while a cathode of the diode 202 is connected with a base terminal ofthe transistor 203 for discharge. Between a collector terminal and anemitter terminal of the transistor 203 for discharge, the capacitor 204for charge and discharge is connected. Further, the emitter terminal ofthe transistor 203 for discharge is connected, in series, with threediodes 205 for potential adjustment. It should be noted that anodeterminals of the diodes 205 for potential adjustment are connected tothe emitter terminal of the transistor 203 for discharge. Due to such aconfiguration, the sawtooth wave generator 20 can generate a sawtoothwave synchronized with the turn-on of the phase-controlled voltage.

[0071] Hereinafter, operations to be performed in the present embodimentwill be briefly described. Note that in the configuration of the presentembodiment, the operation of the discharge lamp is based on the sameprinciple as the first embodiment, and the further description thereofwill be omitted.

[0072] Due to the pulse wave from the photo coupler 19, an output signalof the differentiating circuit 201 becomes a differential wavesynchronized with a rising edge and a falling edge of the pulse wave,and only the differential wave synchronized with the rising edge byusing the diode 202 with a low leakage current is inputted to the baseterminal of the transistor 203. And the capacitor 204 connected betweenthe collector terminal and emitter terminal of the transistor 203repeats charge and discharge using, as a trigger, the rising edge of thepulse wave from the photo coupler 19, thus allowing the generation of asawtooth wave. Further, since the emitter terminal of the transistor 203for discharge is connected with three diodes 205 for potentialadjustment, each having a forward voltage of about 0.6V, for example,the minimum potential of the sawtooth wave becomes about 1.8V, thusmaking it possible to raise the level of a base voltage of the sawtoothwave. Furthermore, since the charge and discharge is carried out using,as a trigger, the signal of the turn-on of the phase-controlled voltage,the sawtooth wave maintains a constant waveform even if the conductionangle of the phase-controlled voltage is changed.

[0073] If the configuration of the second embodiment is adopted, itbecomes possible to implement the sawtooth wave generator 20 withinexpensive components without using any expensive IC components. In thepresent embodiment, although three diodes 205 for potential adjustmentare used, four or more diodes 205 may alternatively be used, or one ortwo diodes 205 may optionally be used. Moreover, instead of the diode, aconstant-voltage power supply may be used. It should be noted that, morefavorably, a buffer circuit is added, thus increasing output impedance.

EMBODIMENT FOR REFERENCE

[0074]FIG. 6 shows a circuit diagram of a device for operating adischarge lamp having electrodes according to an embodiment forreference for purpose of comparison with the embodiments of the presentinvention. The embodiment for reference differs from the above-describedfirst embodiment in that a discharge bulb 17′ has electrodes, and that aload resonant circuit is differently formed for the operation of afluorescent lamp 3′ having electrodes. It should be noted that the sameconstituting elements as the counterparts described in the firstembodiment are identified by the same reference characters, and thefurther description thereof will be omitted.

[0075] In the configuration of the embodiment for reference, as shown inFIG. 6, an LC resonant circuit including: a fluorescent lamp 3′; aresonant inductor 13; a resonant capacitor 15; and a capacitor 14 forresonance and preheat is connected between a drain terminal and a sourceterminal of a MOSFET 12.

[0076] In the configuration of the embodiment for reference, if a highvoltage is generated as a resonance voltage at both ends of thecapacitor 14 of the LC resonant circuit, the temperature of eachelectrode is increased due to a preheat current flowing to the twoelectrodes within the discharge bulb 17′, and if the generation ofthermion from the electrodes is easily allowed, the discharge bulb 17′causes a breakdown and starts discharge. Once the discharge bulb 17′ hasstarted the discharge, the current flowing through the discharge bulb17′ is limited by the resonant inductor 15, thus maintaining the stabledischarge.

[0077] The configuration and operation of a dimming controller 7 of theembodiment for reference are similar to those of the dimming controller7 of the first embodiment. By implementing the configuration of thedischarge lamp operating device as shown in FIG. 6, it becomes possibleto stably carry out dimmable operation of the fluorescent lamp havingelectrodes when the dimming is relatively shallow. However, if deepdimming is carried out, preheating of the electrodes becomesinsufficient and the discharge of electrons is prevented; thus, thelight is abruptly extinguished when it has a certain brightness, and thedimming cannot be smoothly carried out. In this respect, the dischargelamp operating device of the embodiment for reference is different fromthat of the present invention.

[0078] Although the discharge lamp operating device of the embodimentfor reference includes the fluorescent lamp 3′ having electrodes, theballast circuit 4 for carrying out intermittent driving is not verysuitable for use in combination with the fluorescent lamp 3′ havingelectrodes according to the embodiment for reference, but is moresuitable for use in combination with the electrodeless fluorescent lamp3 of the first and second embodiments. This is because since theintermittent driving is an operation that repeats turning-on andturning-off, the electrodes of the fluorescent lamp 3′ are severely wornout, thus causing the problem that their lives are shortened. In thepresent invention, since the electrodeless discharge lamp 3 has noelectrode to begin with, such a problem will not occur.

[0079] It should be noted that in the first embodiment of the presentinvention, the dimming controller 7 is formed so as to output a signalfor synchronizing the timing of the turn-on of the phase-controlledvoltage with that of the operation of the lamp intermittently driven bythe DC-AC converter 6 because dimming operation can be carried out morefavorably if the synchronization is achieved.

[0080] In the configuration shown in FIG. 7, a ballast circuit 4′carries out intermittent driving, but is not intended to synchronize thetiming of the turn-on of the phase-controlled voltage with that of theoperation of the lamp intermittently driven by a DC-AC converter 6. Theconfiguration shown in FIG. 7 differs from that of the first embodimentin that a dimming controller 7′ is formed so as to generate a dimmingcontrol signal and send a dimming command signal to the DC-AC converter(inverter circuit) 6.

[0081] The dimming controller 7′ is made up of: a dimming signalgenerator 74; and a dimming command signal section 10 for sending thedimming command signal to the DC-AC converter 6. An output from a dimmer2, phase-controlled by a triac, is half-wave rectified through ahalf-wave rectifier 71, a comparator 73 compares the resulting outputvoltage (120 Hz) with an output voltage from a triangular wave generator72 for generating a reference voltage with a reference frequency (120Hz), and then the comparator 73 outputs a pulse shape dimming signalwith a constant frequency. The dimming signal is sent to the DC-ACconverter 6 via the dimming command signal section 10, and the dimmingof the electrodeless fluorescent lamp 3 is carried out while the on timeand off time of the DC-AC converter 6 being changed. The electrodelessfluorescent lamp is used as a discharge lamp, the switching frequency f1of the inverter circuit is 200 kHz, and MOSFETs are used as switchingelements.

[0082]FIG. 8 shows experimental results obtained from the configurationshown in FIG. 7. Hereinafter, in addition to the contents shown in FIG.8, the operation and characteristic of the discharge lamp operatingdevice shown in FIG. 7 will be described.

[0083]FIG. 8 illustrates waveform charts showing waveforms a through d,in which each horizontal axis is a time axis, and the time axis servesas a common measure in the respective waveform charts.

[0084] In FIG. 8, a represents the waveform of the voltagephase-controlled in the dimmer 2. As can be seen from this chart, theconduction angle of the triac of the dimmer 2 is close to π, andtherefore, considerably deep dimming is carried out. In FIG. 8, brepresents the dimming command signal that is sent from the dimmingcontroller 7 to the DC-AC converter 6 when the phase-controlled voltagesuch as one having the waveform a in FIG. 8 is inputted to the ballastcircuit 4.

[0085] As can be understood from the comparison made between thewaveforms a and b in FIG. 8, the turn-on of the phase-controlled voltageis not synchronized with the turn-on of the dimming command signal. Thatis, after the turn-on of the phase-controlled voltage, the sending ofthe dimming command signal from the dimming controller 7 to the DC-ACconverter is delayed by a time period Δt. Since a large amount of energyis required for the start of operation of the electrodeless fluorescentlamp 3, a large drain current flows through each of the MOSFETs 11 and12 at the moment of operation of the lamp as indicated by the waveform cin FIG. 8. If the turn-on of the dimming command signal is delayed fromthat of the phase-controlled voltage by the time period Δt, the risingof the drain current of each of the MOSFETs 11 and 12 is delayed. Thus,a period of time during which a high-frequency electric power issupplied to the electrodeless fluorescent lamp 3 and a period of timefor light emission are reduced accordingly, and in addition, the drivingof the DC-AC converter is stopped in the state where thephase-controlled voltage right after the turn-on thereof is at a highestlevel; consequently, a reduction in the light emission output of theelectrodeless discharge lamp is significant.

[0086] If deeper dimming is carried out using the dimmer 2, the draincurrent of each of the MOSFETs 11 and 12 is decreased, and as a result,the high-frequency electric power supplied to the electrodelessfluorescent lamp 3 is reduced, and a threshold state where the lamp isoperated or extinguished is nearly reached.

[0087] In other example, there occurs a time lag as shown in FIG. 9.Also in this example, since the synchronization is not achieved, thehigh-frequency electric power supplied to the electrodeless fluorescentlamp 3 is similarly reduced, and the threshold state where the lamp isoperated or extinguished is nearly reached. In such a state, flickeringor undesirable extinguishing easily occurs, and furthermore, in carryingout deep dimming, the electrodeless fluorescent lamp cannot be operatedat all if the time lag Δt becomes too long.

[0088] According to the present invention, even if such an unstablestate exists, the dimming controller is formed so as to output a signalfor extinguishing the lamp before the operation thereof becomesunstable, and therefore, smooth dimming can be carried out. Furthermore,by achieving the synchronization in this case, it becomes possible toreduce the possibility of reaching the unstable state even if deeperdimming is carried out, and the range in which the actual brightness isvariable (i.e., the range of the actual dimming) can be extendedaccordingly; as a result, a more outstanding dimmable electrodelessdischarge lamp can be implemented, thus providing a preferredembodiment. Specifically, in the discharge lamp operating device (e.g.,the electrodeless self-ballasted fluorescent lamp) described in each ofthe foregoing embodiments, if the voltage phase-controlled by the dimmeris inputted to the fluorescent lamp so that the fluorescent lamp isdimmed, the timing of the turn-on of the phase-controlled voltage issynchronized with that of the turn-on of the intermittent command signalfor intermittently driving the DC-AC converter 6, and the fluorescentlamp can be extinguished before the operation of the discharge lampbecomes unstable due to the approach of the conduction angle of thephase-controlled voltage to π and the resulting reduction of the voltageapplied to the lamp. Consequently, stable dimming operation can beachieved.

[0089] In the inventive electrodeless self-ballasted fluorescent lampand discharge lamp operating device, the dimming controller is formed soas to output a signal for extinguishing the electrodeless fluorescentlamp (or discharge lamp) before the operation of the electrodelessfluorescent lamp (or discharge lamp) becomes unstable, thus making itpossible to achieve smooth dimming operation that causes no flickering.

[0090] Industrial Applicability

[0091] The present invention is effective where it is applied toelectrodeless discharge lamps, and the industrial applicability of thepresent invention is excellent in that an electrodeless self-ballastedfluorescent lamp connected to a dimmer, in particular, can be smoothlydimmed without causing any flickering.

1. An electrodeless self-ballasted fluorescent lamp comprising: anelectrodeless fluorescent lamp; a ballast circuit for applying ahigh-frequency voltage to the electrodeless fluorescent lamp; and a lampbase electrically connected to the ballast circuit, wherein theelectrodeless fluorescent lamp, the ballast circuit and the lamp baseare formed as one unit, wherein the ballast circuit comprises: an AC-DCconverter for converting a phase-controlled AC voltage into a DCvoltage; a DC-AC converter for converting the DC voltage into ahigh-frequency voltage, the DC-AC converter being formed so as tointermittently drive the electrodeless fluorescent lamp due to theexistence of an operating period during which the high-frequency voltageis applied to the electrodeless fluorescent lamp so that theelectrodeless fluorescent lamp is operated, and an extinguishing periodduring which the generation of the high-frequency voltage is stopped sothat the electrodeless fluorescent lamp is extinguished; and a dimmingcontroller formed so as to detect the turn-on of the phase-controlled ACvoltage and output an intermittent command signal that changes the ratiobetween the operating period and the extinguishing period to the DC-ACconverter, and wherein the dimming controller is formed so as to outputa signal for extinguishing the electrodeless fluorescent lamp before theoperation thereof becomes unstable.
 2. The electrodeless self-ballastedfluorescent lamp of claim 1, wherein the dimming controller comprises: afirst dimming control signal input section and a second dimming controlsignal input section; a sawtooth wave generator for generating asawtooth wave; and a dimming command signal generator for generating adimming command signal, wherein the first dimming control signal inputsection is connected to the sawtooth wave generator via a photo coupler,and wherein the second dimming control signal input section is connectedto the dimming command signal generator.
 3. The electrodelessself-ballasted fluorescent lamp of claim 2, wherein the sawtooth wavegenerator and the dimming command signal generator are connected to acomparator.
 4. The electrodeless self-ballasted fluorescent lamp ofclaim 1, wherein the dimming controller is further formed so as tooutput a signal for synchronizing the timing of the turn-on with that ofthe operation of the lamp intermittently driven by the DC-AC converter.5. The electrodeless self-ballasted fluorescent lamp of claim 1, whereinthe dimming controller has a sawtooth wave generator comprising adifferentiating circuit that comprises a capacitor and a resistor,wherein the differentiating circuit is connected to a collector terminalof a transistor for generating a pulse wave synchronized with theturn-on and turn-off of the phase-controlled AC voltage, wherein anoutput terminal of the differentiating circuit is connected with ananode of a diode, while a cathode of the diode is connected with a baseterminal of a transistor for discharge, wherein an emitter terminal ofthe transistor for discharge is connected with a diode for potentialadjustment, and wherein a capacitor for charge and discharge isconnected between the emitter terminal and collector terminal of thetransistor for discharge, thus allowing the generation of a sawtoothwave synchronized with the turn-on of the phase-controlled voltage. 6.The electrodeless self-ballasted fluorescent lamp of claim 1, whereinthe phase-controlled AC voltage is an output voltage of a dimmer whichhas been phase-controlled by the dimmer.
 7. A discharge lamp operatingdevice comprising: a discharge lamp; an AC-DC converter for converting aphase-controlled AC voltage into a DC voltage; a DC-AC converter forconverting the DC voltage into a high-frequency voltage, the DC-ACconverter intermittently driving the discharge lamp due to the existenceof an operating period during which the high-frequency voltage isapplied to the discharge lamp so that the discharge lamp is operated,and an extinguishing period during which the generation of thehigh-frequency voltage is stopped so that the discharge lamp isextinguished; and a dimming controller for detecting the turn-on of thephase-controlled AC voltage and for outputting an intermittent commandsignal that changes the ratio between the operating period and theextinguishing period to the DC-AC converter, wherein the discharge lampis an electrodeless discharge lamp, and wherein the dimming controlleris formed so as to output a signal for extinguishing the discharge lampbefore the operation thereof becomes unstable.
 8. The discharge lampoperating device of claim 7, wherein the dimming controller is furtherformed so as to output a signal for synchronizing the timing of theturn-on with that of the operation of the lamp intermittently driven bythe DC-AC converter.
 9. The discharge lamp operating device of claim 7,wherein the discharge lamp has a discharge bulb having a recessedportion, and wherein an induction coil is inserted into the recessedportion of the discharge bulb.